1. Field of the Invention
The present invention pertains to a color management system which includes a business graphics rendering mode by which print images are rendered with a bright and vivid result. More specifically, in the business graphics rendering mode, overall color contrast of printed images is increased, while the achromatic contrast of the image is left essentially unaltered.
2. Description of the Related Art
Recently, as the availability of color monitors and color printers has increased, it is more and more commonplace for a computer user to display a full color image on a color monitor, such as by using desktop publishing software to display business graphics, photographic images, and the like, and then to request a full color printout of the displayed image.
However, color printers and color monitors form color images differently. Specifically, a color monitor is a light emitting device; colors are formed on color monitors by additive light processing in which light from three color primaries, generally red, green and blue, are added. Printed images, on the other hand, simply reflect ambient light; colors are formed by subtractive light processing according to the way ambient light is affected by three subtractive primaries, generally cyan, magenta and yellow (and sometimes black).
Additive light processing and subtractive light processing are fundamentally different. As a result, the range of colors displayable on a monitor is different from the range of colors printable by a printer. FIG. 1 is the CIE 1931 chromaticity diagram showing the range (or "gamut") of colors displayable by a monitor (area "A") and the range (or "gamut") of colors printable by a printer (area "B"). As seen in FIG. 1, the range of colors displayable on a monitor is generally greater than the range of colors printable by a printer. This is because a monitor is a light emitting device which uses color primaries that differ from those of a printer, and thus has a larger range of reproducible colors. There are, however, some colors such as at area 10 where a printed image, which uses light-subtractive primaries, can reproduce colors that a monitor cannot.
Because of the difference between the gamuts of printable and displayable colors, it has heretofore been difficult to print color images which are perceived by a viewer as faithful reproductions of color images displayed on a monitor. Specifically, it is simply not possible to print a color in areas like out-of-gamut area 11 which are outside the range "B" of printable colors. Accordingly, even though those colors may be seen on color monitors, they cannot be printed on a color printer.
To complicate an already complicated situation, what a viewer perceives as a faithful printed reproduction of displayed image often varies based on the nature of the printed matter. For example, in a situation where photographs or the like are printed, overall image quality and naturally-varying colors are more important than an exact colorimetric match between displayed and printed colors. Similarly, in situations where color uniformity is required such as in reproduction of corporate logos and the like, accurate colorimetric reproduction is more important than other factors. And, in the case of business graphics such as pie charts and bar graphs and the like, vividness of color--particularly fully-saturated colors like the red, green and blue colors indicted respectively at 12, 13 and 14 in FIG. 1--is more important than accurate color reproduction.
Because of these factors, not only is accurate color impossible due to the differences between the range of printable and displayable colors, but even good color reproduction is difficult since what is "good" in one situation such as photographic images is not "good" in other situations such as business graphics.
The Intercolor Consortium, which is a group of operating system and color peripheral manufacturers, have issued an "Intercolor Profile Format", Version 3.0 of which, dated Jun. 10, 1994, is specifically incorporated into the subject application. The Intercolor Consortium has attempted to address the foregoing three different situations by defining the need for three different rendering techniques to deal with each of the above-mentioned three different situations. According to the Intercolor Consortium, a "perceptual" color rendering technique is to be used when good overall image quality is desired, such as in photographs; a "colorimetric" rendering technique is to be used when accurate color reproduction is desired, such as in corporate logos or paint chips or the like; and a "saturation" color rendering technique is to be used when color saturation is important, such as in business graphics with pie charts and bar graphs. Various color rendering techniques have since been proposed, each in accordance with "perceptual", "colorimetric", and "saturation" needs, but problems still remain.
Specifically, in a "saturation" color rendering technique, which is hereafter referred to as a "business graphics rendering technique" because of its widespread use in connection with business graphics, in order to increase color saturation, it has been considered simply to increase ink (or toner) amounts for heavily-inked areas, and also to decrease ink (or toner) amount in lightly-inked areas, so as to increase overall contrast of printed images. For chromatic regions of an image, this simple technique results in a more vivid image. However, in achromatic neutrally colored areas of an image, such as in a gray-scale image, such techniques have an undesirable property of completely blackening dark gray areas of the image while completely whitening light gray areas of the image. Accordingly, a need exists for a business graphics rendering mode which provides increased color contrast for business graphics application, while leaving essentially unaltered achromatic neutrally-colored areas of the image.